U.S. patent application number 11/477917 was filed with the patent office on 2007-01-11 for inkjet recording apparatus.
This patent application is currently assigned to RISO KAGAKU CORPORATION. Invention is credited to Hitoshi Arai, Masao Suzuki.
Application Number | 20070008359 11/477917 |
Document ID | / |
Family ID | 37617947 |
Filed Date | 2007-01-11 |
United States Patent
Application |
20070008359 |
Kind Code |
A1 |
Suzuki; Masao ; et
al. |
January 11, 2007 |
Inkjet recording apparatus
Abstract
Disclosed herein is an inkjet recording apparatus including
plural recording heads, each of which has plural nozzles, which
selectively discharge ink, arranged at a predetermined pitch in a
line, the inkjet recording apparatus being constructed such that
the plural recording heads are arranged in a zigzag fashion such
that the disposition direction of the nozzles is parallel with a
main scanning direction, the respective ends of two adjacent
recording heads are overlapped with each other to form a joint
part, and ink from the selected nozzles of the respective recording
heads is discharged on print paper fed along a sub scanning
direction at a predetermined timing corresponding to the positions
of the respective recording heads in the sub scanning direction
such that an in-line image continuous in the main scanning
direction is formed on the print paper, wherein the inkjet
recording apparatus further includes a control unit for controlling
the driving operation of the respective nozzles at the joint part
depending upon the dispositional relation between the nozzles of
the two recording heads at the joint part in the main scanning
direction.
Inventors: |
Suzuki; Masao; (Tokyo,
JP) ; Arai; Hitoshi; (Tokyo, JP) |
Correspondence
Address: |
KANESAKA BERNER AND PARTNERS LLP
SUITE 300, 1700 DIAGONAL RD
ALEXANDRIA
VA
22314-2848
US
|
Assignee: |
RISO KAGAKU CORPORATION
Tokyo
JP
|
Family ID: |
37617947 |
Appl. No.: |
11/477917 |
Filed: |
June 30, 2006 |
Current U.S.
Class: |
347/12 |
Current CPC
Class: |
B41J 2/04586 20130101;
B41J 2/04508 20130101; B41J 29/393 20130101; B41J 2/155 20130101;
B41J 2/04573 20130101 |
Class at
Publication: |
347/012 |
International
Class: |
B41J 29/38 20060101
B41J029/38 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 6, 2005 |
JP |
2005-197740 |
Claims
1. An inkjet recording apparatus comprising a plurality of
recording heads, each of which has a plurality of nozzles, which
selectively discharge ink, arranged at a predetermined pitch in a
line, the inkjet recording apparatus being constructed such that
the plurality of recording heads are arranged in a zigzag fashion
such that a disposition direction of the nozzles is parallel with a
main scanning direction, the respective ends of two adjacent
recording heads are overlapped with each other to form a joint
part, and ink from the selected nozzles of the respective recording
heads is discharged on print paper fed along a sub scanning
direction at a predetermined timing corresponding to positions of
the respective recording heads in the sub scanning direction such
that an in-line image continuous in the main scanning direction is
formed on the print paper, wherein the inkjet recording apparatus
further comprises: a control unit for controlling the driving
operation of the respective nozzles at the joint part depending
upon a dispositional relation between the nozzles of the two
recording heads at the joint part in the main scanning
direction.
2. The inkjet recording apparatus according to claim 1, wherein
when a distance in the main scanning direction at the joint part
between two nozzles located at endmost parts of the two recording
heads, among the nozzles that are to be selected, is less than the
predetermined pitch, the amount of ink less than a normal amount of
ink is discharged from the two nozzles.
3. The inkjet recording apparatus according to claim 1, wherein
when the distance in the main scanning direction at the joint part
between two nozzles located at the endmost parts of the two
recording heads, among the nozzles that are to be selected, is
greater than the predetermined pitch, the amount of ink equal to
the normal amount of ink is discharged from the two nozzles, and
one nozzle of each recording head disposed between the two nozzles
in the main scanning direction is driven such that the amount of
ink less than the normal amount of ink is discharged from the
driven nozzles.
4. The inkjet recording apparatus according to claim 1, further
comprising a memory for storing data on the dispositional relation
at the joint part and positional data of the joint part, the memory
being provided at the recording heads.
5. A color inkjet recording apparatus for discharging different
color inks to common print paper, using a plurality of inkjet
recording apparatuses according to claim 1, which discharge the
different color inks, respectively, to form a full color image on
the common print paper, wherein the plurality of inkjet recording
apparatuses are arranged such that positions of joint parts are
different from each other in a main scanning direction.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an inkjet recording
apparatus including plural recording heads, each of which has
plural nozzles arranged at a predetermined pitch in a line, wherein
the plural recording heads are arranged in a zigzag fashion such
that the recording heads are parallel with a main scanning
direction while ends of the recording heads are overlapped with
each other, and the nozzles of the respective recording heads are
driven at a predetermined timing corresponding to the positions of
the respective recording heads in a sub scanning direction such
that ink is discharged on print paper fed along the sub scanning
direction, thereby forming an arbitrary image including an in-line
image. More particularly, the present invention relates to an
inkjet recording apparatus constructed such that the quality of an
obtained image is not deteriorated at positions corresponding to
joint parts of the recording heads (overlap parts of the nozzle
arrays) of the above-described inkjet recording apparatus even when
assembly error of nozzle pitch occurs at the joint parts.
[0003] 2. Description of the Related Art
[0004] It is economically unreasonable that a head of an inkjet
recording apparatus, which discharges ink from nozzles to form an
image, is constructed as a unitary structure having a length
corresponding to the width of print paper. Consequently,
small-sized recording heads are normally modularized, and plural
modularized recording heads are assembled to construct a
large-sized line head having a desired length.
[0005] For example, Patent Reference 1 discloses an inkjet printing
apparatus including plural inkjet heads, each of which has plural
ink nozzles for discharging ink, wherein the ink nozzles are
arranged at a predetermined interval in a line, and the inkjet
heads are arranged such that the arranging directions of the ink
nozzles coincide with each other in a line. The distance between
the adjacent inkjet heads may be greater or less than the nozzle
pitch of each inkjet head depending upon the assembly accuracy of
the inkjet heads. In this case, however, portions of an image
corresponding to joint parts of the inkjet heads are merely
thickened or thinned by increasing or decreasing the number of ink
drops, and therefore, lines or spots are formed in the obtained
image. In the inkjet printing apparatus disclosed in Patent
Reference 1, the number of ink drops are not merely increased or
decreased depending upon the nozzle pitch at the joint parts of the
inkjet heads, but the number of ink drops is decided such that ink
can be appropriately spread around the joint parts with a
statistically desired concentration by a fuzzy control, without
fixing the number of ink drops. As a result, a regular shape does
not appear at positions of the image formed on print paper, which
correspond to the joint parts of the inkjet heads, and therefore,
lines or spots are not visible.
[0006] [Patent Reference 1] Japanese Unexamined Patent Publication
No. 2005-7582
[0007] In the case that a large-sized inkjet recording apparatus is
constructed by assembling plural small-sized recording heads, which
are modularized, in parallel with each other, when the nozzle pitch
of the respective recording heads, each of which is constructed as
a module, is small, the pitch between the nozzles at the coupling
parts of the adjacent recording heads may not be physically
maintained. In this case, it is impossible to combine the plural
recording heads such that the recording heads are arranged in a
line; however, it is possible to two-dimensionally arrange the
recording heads in a zigzag fashion such that the nozzle arrays of
the respective recording heads are parallel with a main scanning
direction, whereby the nozzle arrays at the corresponding ends of
the adjacent recording heads are overlapped with each other.
[0008] FIG. 1 is a view schematically illustrating the structure of
the above-described inkjet recording apparatus. Plural small-sized
recording heads 1, which are modularized, are prepared, and the
modularized recording heads 1 are arranged side by side in a zigzag
fashion along a main scanning direction (in the right-and-left
direction in the drawing). In the illustrated example, the inkjet
recording apparatus is a single color (for example, black color)
inkjet recording apparatus. Approximately 10 of nozzles are
overlapped at the joint part 2 (the overlap part of the nozzle
arrays) between the adjacent recording heads 1 (modules).
Approximately five of the nozzles, among approximately ten of the
nozzles, which are overlapped at the joint part 2, are continuous
with the nozzles, which are not overlapped, of one of the adjacent
recording heads 1, and therefore, approximately five of the front
nozzles, which are arranged before the above-mentioned nozzles, are
not used. Approximately five of the remaining nozzles, among
approximately ten of the nozzles, which are overlapped at the joint
part 2, are continuous with the nozzles, which are not overlapped,
of the other of the adjacent recording heads 1, and therefore,
approximately five of the front nozzles, which are arranged before
the above-mentioned nozzles, are not used. Consequently, the
distance between the nozzles, which are used, at the ends of the
respective recording heads 1 becomes equal to the distance between
the nozzles of the recording heads 1.
[0009] In the inkjet recording apparatus in which the plural
modularized recording heads 1 are arranged in a zigzag fashion
along the main scanning direction as described above, print paper 3
is fed in the sub scanning direction (in the upward-and-downward
direction in FIG. 1), ink is discharged from the respective nozzles
selected from the respective recording heads 1 to the print paper 3
at a predetermined timing corresponding to the positions of the
respective recording heads in the sub scanning direction, whereby
an in-line image continuous in the main scanning direction is
formed on the print paper 3, which will be described below in
detail.
[0010] First, as shown in FIG. 2A, ink is discharged (printing is
performed) from recording heads 1a, which are located at the front
part in the sub scanning direction (in the paper feeding
direction). Subsequently, as shown in FIG. 2B, ink is discharged
from recording heads 1b, which are located at the rear part in the
sub scanning direction, at the time when the print paper 3 has been
fed by the separation distance of the recording heads 1 in the sub
scanning direction from the state shown in FIG. 2A. As a result, as
shown in FIG. 2C, an in-line image continuous in the main scanning
direction, is formed on the print paper 3.
[0011] In the case that the plural recording heads 1 are arranged
such that the recording heads 1 are overlapped with each other at
the joint parts in the main scanning direction, however, it is
necessary that the plural recording heads 1 be arranged in a
two-dimensional plane in a zigzag fashion along the main scanning
direction as described above. Especially, it is necessary that the
respective recording heads 1 be arranged and assembled with high
accuracy such that the nozzle pitch between the adjacent recording
heads 1 at the joint part 2 is equal to the pitch of the respective
recording heads 1.
[0012] Furthermore, a step may occur between the recording heads 1
and 1 even in the sub scanning direction depending upon the
accuracy of the disposition of the recording heads 1 and the
accuracy of the feeding of the paper. The following description
will be given in consideration of the fact that misalignment occurs
at the joint part 2 in the sub scanning direction.
[0013] FIGS. 3A to 3C are enlarged views illustrating images
entirely printed on the print paper 3 by the inkjet recording
apparatus shown in FIG. 1. In the drawings, the circles indicates
dots formed on the print paper 3 by ink drops discharged from one
nozzle. Dots formed by one of the recording heads are indicated in
outline, and dots formed by the other recording head are indicated
in light black. In FIGS. 3A to 3C, nine enlarged images are shown
by the combination of assembly error states and misalignments in
the sub scanning direction (the middle parts have no misalignment,
and the upper and lower parts have misalignments in opposite
directions).
[0014] When the assembly error in the main scanning direction at
the joint part 2 of the above-mentioned adjacent recording heads 1
is 0, as shown in FIG. 3A, the deterioration of the quality of the
image at the position corresponding to the middle joint part 2 does
not occur even though the misalignment occurs in the sub scanning
direction. However, when the distance between the nozzles in the
main scanning direction at the joint part 2 of the adjacent
recording heads 1 is decreased, as shown in FIG. 3B, the
concentration of the overlapped portions of the dots becomes thick,
and therefore, a black straight line is formed in the sub scanning
direction. Also, when the distance between the nozzles in the main
scanning direction at the joint part 2 of the adjacent recording
heads 1 is increased, as shown in FIG. 3C, the concentration of the
separated portions of the dots does not appear, and therefore, a
white straight line is formed in the sub scanning direction. These
are important factors that are visibly prominent, and therefore,
deteriorate the quality of the image, which are necessary to be
improved.
[0015] A method of adjusting the assembly error to "0" may be
embodied by providing a structure in which the positions of the
respective recording heads 1 constituting the line head can be
adjusted, and performing the adjustment during the assembly
process. However, it is necessary that the plural recording heads 1
be arranged in a zigzag fashion, in two dimensions, and with high
accuracy, as described above. For this reason, the adjustment costs
are greatly increased. Consequently, the adjustment is actually
carried out with appropriate accuracy.
SUMMARY OF THE INVENTION
[0016] Therefore, the present invention has been made in view of
the above problems, and it is an object of the present invention to
provide an inkjet recording apparatus including plural recording
heads 1, which are arranged in a zigzag fashion such that the
recording heads 1 are parallel with a main scanning direction while
adjacent ends of the recording heads are overlapped with each
other, and the nozzles of which are driven at a predetermined
timing corresponding to the positions of the respective recording
heads 1 in a sub scanning direction such that ink is discharged on
print paper 3 fed along the sub scanning direction, and therefore,
an arbitrary image is formed on the print paper, wherein the
quality of an image is not deteriorated, at positions on the print
paper 3 corresponding to joint parts 2 of the recording heads 1
(overlap parts of the nozzle arrays), by appropriately controlling
the discharge of ink from the nozzles even when plus or minus
assembly error of nozzle pitch occurs at the joint parts.
[0017] In accordance with one aspect of the present invention, the
above and other objects can be accomplished by the provision of an
inkjet recording apparatus including plural recording heads 1, each
of which has plural nozzles, which selectively discharge ink,
arranged at a predetermined pitch in a line, the inkjet recording
apparatus being constructed such that the plural recording heads 1
are arranged in a zigzag fashion such that a disposition direction
of the nozzles is parallel with a main scanning direction, the
respective ends of two adjacent recording heads 1 are overlapped
with each other to form a joint part 2, and ink from the selected
nozzles of the respective recording heads 1 is discharged on print
paper 3 fed along a sub scanning direction at a predetermined
timing corresponding to positions of the respective recording heads
in the sub scanning direction such that an in-line image continuous
in the main scanning direction is formed on the print paper 3,
wherein the inkjet recording apparatus further includes: a control
unit for controlling the driving operation of the respective
nozzles at the joint part 2 depending upon a dispositional relation
between the nozzles of the two recording heads 1 at the joint part
2 in the main scanning direction.
[0018] When a distance in the main scanning direction at the joint
part 2 between two nozzles located at endmost parts of the two
recording heads 1, among the nozzles that are to be selected, is
less than the predetermined pitch, an amount of ink less than a
normal amount of ink is discharged from the two nozzles.
[0019] When the distance in the main scanning direction at the
joint part 2 between two nozzles located at the endmost parts of
the two recording heads 1, among the nozzles that are to be
selected, is greater than the predetermined pitch, the amount of
ink equal to the normal amount of ink is discharged from the two
nozzles, and one nozzle of each recording head 1 disposed between
the two nozzles in the main scanning direction is driven such that
the amount of ink less than the normal amount of ink is discharged
from the driven nozzles.
[0020] The inkjet recording apparatus further includes: a memory
for storing data on the dispositional relation at the joint part 2
and positional data of the joint part 2, the memory being provided
at the recording heads 1.
[0021] In accordance with another aspect of the present invention,
there is provided a color inkjet recording apparatus for
discharging different color inks to a common print paper, using the
plural above-described inkjet recording apparatuses, which
discharge the different color inks, respectively, to form a full
color image on the common print paper 3, wherein the plural inkjet
recording apparatuses are arranged such that the positions of the
joint parts 2 are different from each other in the main scanning
direction.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The above and other objects, features and other advantages
of the present invention will be more clearly understood from the
following detailed description taken in conjunction with the
accompanying drawings, wherein:
[0023] FIG. 1 is a typical plan view illustrating the fundamental
structure of a line head of an inkjet recording apparatus according
to a first embodiment of the present invention;
[0024] FIGS. 2A to 2C are views illustrating the formation of an
image performed by the line head shown in FIG. 1;
[0025] FIGS. 3A to 3C are views illustrating the results of the
formation of images performed by the line head shown in FIG. 1 in
the case that joint correction has not been carried out;
[0026] FIGS. 4A to 4C are enlarged views of a joint part of the
line head shown in FIG. 1;
[0027] FIGS. 5A to 5C are views illustrating a method of correcting
the joint part of the line head shown in FIG. 1;
[0028] FIGS. 6A to 6C are views illustrating the results of the
formation of images performed by the line head shown in FIG. 1 in
the case that joint correction has been carried out;
[0029] FIG. 7 is a typical plan view illustrating the fundamental
structure of a line head of an inkjet recording apparatus according
to a second embodiment of the present invention; and
[0030] FIG. 8 is a block diagram typically illustrating an example
of a control system of the inkjet recording apparatus according to
the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0031] Now, preferred embodiments of the present invention will be
described in detail with reference to the accompanying drawings,
i.e., FIGS. 1 to 8.
(1) First Embodiment (FIGS. 1 to 6)
[0032] The inkjet recording apparatus according to this embodiment
has a line head constructed in the same fundamental structure as
that previously described with reference to FIG. 1. Specifically,
the line head of the inkjet recording apparatus includes plural
recording heads 1, each of which has plural nozzles, which
selectively discharge ink, arranged at a predetermined pitch in a
line, wherein the plural recording heads 1 are arranged in a zigzag
fashion such that the arrangement direction of the nozzles is
parallel with a main scanning direction, and the corresponding ends
of two adjacent recording heads 1 and 1, which are adjacent to each
other in the zigzag fashion, are overlapped with each other in the
main scanning direction such that a joint part 2 is formed at the
corresponding ends of the two adjacent recording heads 1 and 1,
whereby the line head has a predetermined length in the main
scanning direction (the lateral direction of print paper 3). Also,
the print paper 3 is fed along the sub scanning direction by a
paper feeding unit (not shown), and the respective recording heads
of the line head are driven such that the driving operation of the
recording heads is synchronous with the feeding operation of the
paper, whereby ink is discharged from the selected nozzles at a
predetermined timing corresponding to positions of the respective
recording heads 1 in the sub scanning direction, and therefore, an
arbitrary image, including an in-line image continuous in the main
scanning direction, is formed on the surface of the print paper
3.
[0033] As shown in FIG. 8, the line head 10, which includes the
plural recording heads 1, and the paper feeding unit 5 are
controlled by a control unit 6 (CPU) such that the operation of the
recording heads 1 is synchronous with the operation of the paper
feeding unit 5. Programs for controlling the feeding operation of
the print paper 3 and the driving operation of the line head 10 are
contained in a read-only memory (ROM) 7 of the control unit 6.
Also, correction driving data inherent in the line head 10 is
contained in the ROM 7 of the control unit 6. The correcting
driving data is set depending upon the assembly accuracy or the
nozzle pitch at the several joint parts 2 of the line head 10,
which includes the plural recording heads 1 arranged in the zigzag
fashion such that the recording heads 1 are overlapped with each
other as in this embodiment. The correcting driving data is used to
correct the amount of ink discharged from the nozzles of the joint
parts 2 such that the printing quality on the positions of the
print paper 3 corresponding to the joint parts is not deteriorated.
That is, the line head 10 of the inkjet recording apparatus
according to this embodiment has the plural recording heads 1,
which are arranged in the zigzag fashion, and the joint parts 2 are
located between the adjacent recording heads 1. However, the
correction driving data inherent in the respective joint parts 2 is
provided.
[0034] In this embodiment, the correction driving data is prepared
as follows, and is stored into the ROM 7 of the control unit 6.
First, after the line head 10 is assembled, the assembled line head
10 is mounted to a printing part of the inkjet recording apparatus,
and a printing operation is performed with respect to the print
paper 3 by discharging ink to the print paper 3 while the print
paper 3 is fed, whereby an image is formed on the print paper 3.
Subsequently, the quality of the obtained image is analyzed to
confirm the assembly accuracy of the respective joint parts 2 of
the line head 10 (the dispositional relation between the nozzles of
the two recording heads 1 at the corresponding joint part 2).
Specifically, as previously described with reference to FIGS. 3A to
3C, any one of the state that the assembly error has not occurred
at the respective joint parts as shown in FIG. 3A, the state that
the distance between the dots is narrow at the respective joint
parts as shown in FIG. 3B, and the state that the distance between
the dots is wide at the respective joint parts as shown in FIG. 3C
appears on the print paper 3. Consequently, it is possible that the
state of the respective joint parts 2 is determined, the correction
driving data of the nozzles, which decides the amount of ink
discharged, which is suitable to the determined state, is chosen,
and the chosen correction driving data is stored in the ROM 7, for
example, in a table-type structure in response to the respective
joint parts 2.
[0035] FIGS. 4A to 4C are enlarged views illustrating the
occurrence of assembly errors at the respective joint parts 2 of
the line head 10 of the inkjet recording apparatus according to
this embodiment. When the driving data is not corrected, the
printing results as shown in FIGS. 3A to 3C are obtained by the
arrangement of the nozzles. When the driving data is corrected as
needed as will be described below, on the other hand, the printing
is performed as typically illustrated in FIGS. 5A to 5C, which will
be described below, and the image to be printed is corrected in
response to the assembly errors, whereby the printing results
respectively shown in FIGS. 6A to 6C are obtained, which will be
described below.
[0036] Also, FIGS. 4B and 4C illustrate two cases that the
overlapped states at one of the two recording heads 1 overlapped
with each other at the joint part 2 (the lower parts of the
drawings) are different by one nozzle pitch from each other. FIG. 6
illustrates the state of dots constituting an image in the same
manner as FIG. 3.
[0037] First, when the distance P in the main scanning direction at
the joint part 2 between one nozzle located at the endmost part of
one of the recording heads 1 and one nozzle located at the endmost
part of the other recording head 1, among the nozzles (shown in
black circles) that are to be selected and driven, is equal to the
nozzle pitch of the respective recording heads 1, as shown in FIG.
4A, the assembly error does not occur at the respective joint parts
2 of the line head 10. In this case, when the printing is performed
on the entire surface of the print paper 3, the result as shown in
FIG. 3A is obtained, and therefore, a significant difference is not
generated, at least, in the main scanning direction, and a line
does not appear in the sub scanning direction. Consequently, in
this case, the correction of the driving data of the nozzles of the
joint part 2 is not necessary.
[0038] When this printing result is enlarged and shown in the shape
of dots, as shown in FIG. 5A, the respective dots are regularly
arranged in a predetermine pitch. However, the difference in the
sub scanning direction is not shown in FIG. 5A. Even when the image
is shown in the state that the difference in the sub scanning
direction occurs, a line, which deteriorates the quality of the
image, does not appear on the image as shown in FIG. 6A.
[0039] Next, it is assumed that the distance in the main scanning
direction at the joint part 2 between one nozzle located at the
endmost part of one of the recording heads 1 and one nozzle located
at the endmost part of the other recording head 1, among the
nozzles (shown in black circles) that are to be selected and
driven, is A, as shown in FIG. 4B. Also, it is assumed that the
distance between the nozzle located at the end of one of the
recording heads 1 (the nozzle located at the end of the lower
recording head 1 in the drawing) and the unselected nozzle adjacent
to the nozzle located at the end of the other recording head 1 is
B, as shown in FIG. 4B. When A>B, the assembly error occurs in a
state that the joint part 2 is narrow. In this case, when the
printing is performed on the entire surface of the print paper 3
without correcting the driving data, the result as shown in FIG. 3B
is obtained, and therefore, a black line appears at the position of
the print paper 3 corresponding to the joint part 2 along the sub
scanning direction. Consequently, it is necessary to correct the
driving data of the nozzle of the joint part 2, which will be
described below.
[0040] As shown in FIG. 5B, distance between two dots, which belong
to the respective recording heads, and formed by the nozzles
located at the adjacent two ends at the joint part 2, among plural
dots (pixels) formed by two recording heads 1 and 1, which are
expected to be arranged at a predetermined pitch in a line along
the main scanning direction, becomes less than the predetermined
pitch under the above-mentioned condition, i.e., under the
condition of A>B, and therefore, the distance between the
above-mentioned two dots is decreased by half of the predetermined
pitch to the minimum. When the normal amount of ink is discharged
in this state, two dots having a normal size are overlapped with
each other on the print paper 3. As a result, a black line occurs
as described above. Consequently, in this case, the inkjet
recording apparatus is driven using the correction driving data to
reduce the amount of ink discharged from the two nozzles located at
the endmost parts of the recording heads corresponding to the two
dots to 75% of the normal amount of ink. Specifically, the distance
between the two dots is decreased by 0.5 pitch to the minimum, and
therefore, the distance between the dots is decreased such that the
sum of the amounts of ink for the two dots is 1.5 (0.75+0.75=1.5),
whereby the increase of concentration caused by the decrease of the
distance between the dots is corrected.
[0041] When the printing result obtained through the driving
operation using the correction driving data is enlarged and shown
in the shape of dots, as shown in the lower part of FIG. 5B, two
dots corresponding to the joint part 2 are overlapped with each
other in the case that no difference occurs in the sub scanning
direction. However, these two dots are smaller than the other dots,
and therefore, the quality of the image is not generally
deteriorated at the position of the print paper corresponding to
the joint part 2. Even when the image is shown in the state that
the difference in the sub scanning direction occurs, a line, which
deteriorates the quality of the image, does not appear on the image
as shown in FIG. 6B.
[0042] Next, the case shown in FIG. 4C illustrates that any one of
one nozzle located at the endmost part of one of the recording
heads 1 and one nozzle located at the endmost part of the other
recording head 1, among the nozzles (shown in black circles) that
are to be selected and driven, at the joint part 2 (the nozzle
located at the end of the lower recording head 1 in the drawing),
is displaced in the direction in which one nozzle is spaced further
apart from the other nozzle along the main scanning direction than
the unselected nozzle adjacent to the nozzle located at the end of
the other recording head 1. Here, it is assumed that the distance
in the main scanning direction between the unselected nozzle
adjacent to the nozzle located at the end of one of the recording
heads 1 and the nozzle of the other recording head 1 is A. Also, it
is assumed that the distance between the unselected nozzle adjacent
to the nozzle located at the end of one of the recording heads 1
and the unselected nozzle adjacent to the nozzle located at the end
of the other recording head 1 is B. When A<B, the assembly error
occurs in a state that the joint part 2 is wide. In this case, when
the printing is performed on the entire surface of the print paper
3 without correcting the driving data, the result as shown in FIG.
3C is obtained, and therefore, a white line appears at the position
of the print paper 3 corresponding to the joint part 2 along the
sub scanning direction. Consequently, it is necessary to correct
the driving data of the nozzle of the joint part 2, which will be
described below.
[0043] As shown in FIG. 5C, the distance between two dots, which
belong to the respective recording heads, and formed by the nozzles
located at the adjacent two ends at the joint part 2, among plural
dots (pixels) formed by two recording heads 1 and 1, which are
expected to be arranged at a predetermined pitch in a line along
the main scanning direction, becomes greater than the predetermined
pitch under the above-mentioned condition, i.e., under the
condition of A<B, and therefore, the distance between the
above-mentioned two dots is increased by half of the predetermined
pitch to the maximum. When the normal amount of ink is discharged
in this state, two dots are normally printed on the print paper 3.
However, the distance between the two dots is excessively wide. As
a result, a white line occurs as described above. Consequently, in
this case, the inkjet recording apparatus is driven using the
correction driving data to maintain the amount of ink discharged
from the nozzles located at the two ends of the recording heads
corresponding to the two dots to the normal amount of ink, and to
drive the unselected nozzles adjacent to the nozzles located at the
two ends such that 25% of the normal amount of ink can be
discharged from the unselected nozzles. Specifically, the distance
between the two dots is increased by 0.5 pitch to the maximum.
Consequently, the amount of ink for the two dots is not changed,
and the two additional dots located in the widened part are formed
by a small amount of ink, such that the sum of the amounts of ink
for the two dots is 2.5 (1.25+1.25=2.5), whereby the decrease of
concentration caused by the increase of the distance between the
dots is corrected.
[0044] When the printing result obtained through the driving
operation using the correction driving data is enlarged and shown
in the shape of dots, as shown in the lower part of FIG. 5C, two
dots corresponding to the joint part 2 are formed while being
spaced a distance greater than the predetermined pitch from each
other in the case that no difference occurs in the sub scanning
direction. However, the two dots, which are formed using 25% of the
amount of ink (concentration), are added in the widened part to
correct the distance, and therefore, the quality of the image is
not generally deteriorated at the position of the print paper
corresponding to the joint part 2. Even when the image is shown in
the state that the difference in the sub scanning direction occurs,
a line, which deteriorates the quality of the image, does not
appear on the image as shown in FIG. 6C.
(2) Second Embodiment (FIG. 7)
[0045] As shown in FIG. 7, the inkjet recording apparatus according
to this embodiment includes four line heads 10, one of which has
been previously described in connection with the first embodiment
of the present invention. The respective line heads 10 are
constructed such that different color inks can be discharged from
the respective line heads 10. In this embodiment, four color inks
include cyan C, magenta M, yellow Y, and blue B, which are printed
on print paper while being overlapped with each other, whereby a
full color image is formed on the print paper.
[0046] The respective line heads 10 are arranged along the feeding
route of a common printing paper 3 such that main scanning
directions are parallel with each other while the respective line
heads 10 are spaced a predetermined interval in the feeding
direction of the print paper 3 (in a sub scanning direction). Also,
the respective line heads 10 are constructed such that the
positions of the joint parts 2 are different from each other in a
main manipulating direction. Specifically, as shown in FIG. 7, the
overlapped parts of the recording heads 1 of the respective line
head 10 are the same, but pluralities (in this embodiment, 10 for
each recording head 1) of nozzles included in the overlapped parts
correspond to the adjacent recording heads 1 in different
manners.
[0047] This embodiment includes the same control unit as shown in
FIG. 8. The four line heads 10 are controlled by the control unit
at an appropriate timing such that the operation of the line heads
10 are synchronous with the feeding operation of the print paper 3.
The driving data, which drives the respective line heads 10, is
image data for the respective colors corresponding to the
respective ink colors obtained through the color separation of the
full color image. In the same manner as in the first embodiment,
the correction is performed based upon the correction driving data
inherent in the joint parts 2 of the respective line heads 10.
[0048] Consequently, according to this embodiment, when the full
color image is formed, the deterioration of the quality of the
image at the joint parts 2 of the respective line heads 10 is low.
Furthermore, the joint parts 2 of the respective line heads 10 are
not overlapped with each other in the sub scanning direction. As a
result, influence due to the joint parts of the respective line
heads 10 becomes further insignificant, and therefore, it is
possible to obtain a good-quality full color image.
[0049] According to the present invention, the number of the
nozzles, to which the correction of the driving operation is
actually performed, in the joint part 2 of the two recording heads
1 arranged adjacent to each other in the zigzag fashion is small,
for example, at most approximately two. Consequently, when
approximately 10 of the nozzles are overlapped with each other at
the joint part 2, the positions of the nozzles, to which the
correction of the driving operation is performed, among them, can
be set in the main scanning direction with considerably high
freedom, and therefore, it is possible to change the joint position
in the color inkjet apparatus that discharges the plural color inks
from the plural line heads 10 as in this embodiment.
[0050] In the above-described embodiments, the joint state of the
respective line heads 10 is detected through a test printing,
correction driving data inherent in the respective line heads 10 is
obtained based on the detected joint state, and the obtained
correction driving data is stored in the memory of the control unit
6. However, this information may be provided at the line heads 10
side such that the information can be read out by the control unit
6 side at any time, and the read-out information can be used to
perform the controlling operation. Specifically, it is possible
that data on the dispositional relation between the nozzles at the
joint part 2 of the line head 10 and positional data of the
corresponding joint part 2 are stored in the memory, the memory is
provided at the recording heads 1, the control unit 6 reads out
data from the memory of the line head 10, the driving data is
corrected by the read-out data, and then the printing operation is
performed.
[0051] Although the joint state of the respective line heads 10 is
detected through the test printing in the above-described
embodiments, it is also possible that the joint part 2 of the line
head 10 is directly observed, using a microscope, to detect the
joint state of the nozzles.
[0052] As apparent from the above description, the present
invention has the following effects.
[0053] In the case that the positional difference, which
deteriorates the quality of the image, occurs at the joint part 2
due to the assembly of the recording heads 1 when the inkjet
recording apparatus according to the present invention is
manufactured, it is confirmed, by performing a test printing on the
print paper 3, whether the positional difference is caused due to
the increase or the decrease of the nozzle pitch, and the driving
state (the amount of ink discharged) of the respective recording
heads 1 is set by the control unit of the inkjet recording
apparatus based on the confirmation.
[0054] Specifically, when the positional difference is less than
the nozzle pitch at the joint part 2, the respective nozzles of the
adjacent two recording heads 1 arranged in a small pitch in the
main scanning direction at the joint part 2 are driven such that
the amount of ink less than the amount of ink discharged from the
nozzles arranged in the regular pitch is discharged from the
nozzles of the adjacent two recording heads 1 arranged in the small
pitch, whereby the driving information of the corresponding
nozzles, which is stored in the control unit, is set. When the
above-mentioned correction is applied to the control of the ink
discharge by the control unit, the pitch between the two dots
corresponding to the joint part 2 is small, during the printing
operation of the inkjet recording apparatus, as compared to the
pitch between the regular dots arranged on the print paper 3 in the
main scanning direction. As a result, the concentration is
increased, and therefore, a black line is formed on the print paper
3 corresponding to the joint part 2 in the sub scanning direction.
According to the present invention, however, the diameter of dots
formed by the ink drops is decreased at the joint part 2 having the
decreased pitch, and therefore, the concentration is decreased.
Consequently, no black line is formed on the print paper 3
corresponding to the joint part 2 along the sub scanning
direction.
[0055] Also, when the positional difference is greater than the
nozzle pitch at the joint part 2, the respective nozzles of the
adjacent two recording heads 1 arranged in a large pitch in the
main scanning direction at the joint part 2 are driven such that
the same amount of ink as the amount of ink discharged from the
nozzles arranged in the regular pitch is discharged from the
nozzles of the adjacent two recording heads 1 arranged in the small
pitch. In addition to this, one nozzle belonging to each recording
head 1 and arranged inside each of the above-mentioned nozzles
having the positional difference is added as a nozzle to be driven,
and the added nozzles are driven such that the amount of ink less
than the amount of ink discharged from the nozzles arranged in the
regular pitch is discharged from the nozzles of the added nozzles.
Driving information to drive the respective nozzles of the
recording heads 1 as described above is stored in the memory of the
control unit. When the above-mentioned correction is applied to the
control of the ink discharge by the control unit, the pitch between
the two dots corresponding to the joint part 2 is large, during the
printing operation of the inkjet recording apparatus, as compared
to the pitch between the regular dots arranged on the print paper 3
in the main scanning direction. As a result, the representation of
the concentration is not possible, and therefore, a white line is
formed on the print paper 3 corresponding to the joint part 2 in
the sub scanning direction. According to the present invention,
however, the dots having a small dot diameter are additionally
formed at the joint part 2 having the increased pitch, and
therefore, the appropriate concentration is represented at the
white part on the print paper 3. Consequently, no white line is
formed on the print paper 3 corresponding to the joint part 2 along
the sub scanning direction.
[0056] As described above, the inkjet recording apparatus according
to the present invention has the plural joint parts between the
recording heads 1 and 1. However, the state of the nozzle pitch is
confirmed for the respective joint parts 2, and control information
corresponding to the positions and states of the joint parts 2 is
stored in the memory of the control unit. Consequently, even though
the assembly accuracy of the recording heads 1 is lowered, any
defect caused due to the nonuniformity of the nozzle pitch does not
occur on a image, and therefore, it is possible to obtain a quality
image. In other words, it is unnecessary to perform the arrangement
and alignment of the recording heads 1 with high costs and high
accuracy when the inkjet recording apparatus is assembled. Also,
even when the assembly error occurs, it is unnecessary to perform
the adjustment with high costs. According to the present invention,
it is possible to obtain a quality image by assembling the
recording heads with allowable costs and appropriate accuracy and
storing the driving correction control data corresponding to the
assembly state and the assembly accuracy in the control unit.
[0057] Also, in the inkjet recording apparatus according to the
present invention, data on the dispositional relation between the
nozzles at the respective joint parts 2 is previously stored in the
memory, and the memory is provided at the corresponding joint part
2. Consequently, when the inkjet recording apparatus is connected
to a control apparatus, the above-mentioned data stored in the
memory is automatically transmitted to the control unit such that
the data can be used to perform the control operation, and
therefore, it is possible to perform the correction control of the
ink discharge depending upon the assembly states of the joint parts
2.
[0058] Furthermore, in the case that plural inkjet recording
apparatuses, which are provided for plural different colors, are
prepared to construct a full color printing apparatus, the plural
inkjet recording apparatuses are arranged such that the positions
of the joint parts 2 are different from each other in the main
manipulating direction, whereby influence of the respective colors
of the full color image on the joint parts 2 is decreased, and
therefore, it is possible to provide an image having a natural
quality in appearance.
[0059] Although the preferred embodiments of the present invention
have been disclosed for illustrative purposes, those skilled in the
art will appreciate that various modifications, additions and
substitutions are possible, without departing from the scope and
spirit of the invention as disclosed in the accompanying
claims.
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